freedman



May 23, 1950 c. L. FREEDMAN ELECTRODYNAMOMETER Filed July 20, 1946INVENTOR fididzz A RNEY Patented May 23, 1950 o STATES PATENT OFF-ICE25081379 .EIJEGTRODYNAMOMETER;

Cecil .L.- Freedman, Pittsburgh,- Ifa; assignor to Westinhouse ElectricGotl wation, East Pittsburzh, Pa, a cor oration of Pennsylvania IMplication July 20, 1946'98331421 No} 685,056 (01. 171-95) I1 Claims. 1

invention relates to electricai-instruments,. and ithasparticularrelation toelectriealmeasuring instruments or the .electrodynamic type:

Inv'the electrical industry it is'frequently necessary ordesirablethatfinstruments .be provided which are responsive to:quantities-in polyphase and three wire' --alternat-ing'--1currentcircuits and toquen-tities in' three-wire .vdirect-current circuits.Suchinstruments 'may take the form of two-ele ment electredynamicinstruments having two complete elements with both of the moving coilsofthe elements mounted on a common shaft. Conventional prior arttwo-element electrody namic instrumentsegenemlly employed no iron coresbecause t constructional difliculties and; because of errorsintroducedby the utilization oii-rontifor the cores. Adiscussion ofelectrod'ynanaic or dynamometer instruments will found in volumelpIElectrical-Measuring Instruments by firysdaleandilolley published in1924 by 15. Van Nostrand" U'ompany N'ewYbrk city. The discussionispresentedlinchapter 'VITI' anc'lLtwo-ehment or double walttfiietersare treated in a section beginning on page 341'. V V p p H In. the Lunasapplication, Serial No. 570,028, filed December 2T,. "1"944,atwo-elemente'lectrodynarnic li'fnstrulnelt is disclosed which has iron Gore's;Thesetiirorr cor s are so constructedtha't the'rotor assemtly of theinstrument can be removed from the .st'atorassefiikily withoutdisturbmetricironwresimanywaty. .Fll'lthflildrllflnas provide animproved electrodynamic electricaldiscloses the provision of rei'rerselyasfsbciatedirori coreswnien jprodiiceopposedisolenoid forces act'-i'rfg" ontii'e m"'ovin"g chil asse' 'm"" b1y 'Cbfisequejritly; errorsresulting from 'sole'zidiii ac'tlon are reduced or substantiallyeliminated. Referen' ce" also may heniacfe tytne"application-$ 13. A.Young et s11, I

Serial no. "B'ODBB'GQfIled "sestemtem; i943", new Patent-Nb; 27, is'sued'fiarch" 1 6, T948; Bo'tn or tlie aroresami appiieatiorisrand themesentanplica'tibmare 'asslgne'i'to the same" assignee;

' aecorda rce witn the invention, compact coplanar electrddyfiafific"iifi's tfilhi'efit 'plovidedf' which is suitable forreplacing"priorart;tvvti ele merit eie'ctrodynamizr instruments. Thejinvem new ontempiietestneprevlsitrsdra mtvifig coii assembly lieriiicoil sides are mummydispraeed abontia commonportionw mana.-

lifitfhe coil' siiles "as an independent magnetiezneldprevmedbyindepenee" fit mag netlcipatli ammueian eiirs weenie: associatedOOiliSidB: Th megnetioiapaths are se configured that the moving icoil orrotor assemblyrm y'be re movedeiromthetassociatedistator assembly"without disturbing'the maeneticistructure inearly way; Solenoid:actlontis tr'eduoed ortsubstantially elimi nated by divlding themagnetic structure intosections whichaapply opposed solenoid-forcestotheriotorvasseniblys.

instrument suitable for replacing prior art two-= element electrodynamicinstruments;

It'i-s another-object of the invention to provide" anelectrodynamicinstrument having a; moving coil assembly wherein twocoilsides are align-'- larly displaced about a common portion ofan axisfor energization; respectively, by independent magnetic fields.

It is an additional object of the invention to provide anelectrodynamic'instrument having a single coil mounted .for rotationabout anaxis in-' termediate two sides of the coil and provided with anindependent magnetic field for each side of the coil.-

lt-i'sa' furtherobiectof the invention to pro vide amelectrodynamicinstrument having a mow lng coil assembly whereintwo coil-sidesareangu-= larly displacedebouta common'portionofanaxis; wherein aseparate magnetic field: is provided foreachor the coil sides; and:wherein amagnetic structure is provided which is configured-towermitremoval of the coil-assembly therefrom-withou-tdisturbing themagnetic structure.

It'is' also an objectof the-invention:totprovide an-electrodynamicinstrument having a moving coil assembly providing two' coilsidesdisposed angular-1yaboutascommon portion of an axis andhaving aseparatemagnetic fieldior each of the coil sides, with-a magnetic structureconfiguredtosubstantl-afly eliminate solenoid a'ction betweenthemagnetic structure and themoving coil -assembly.

Other objects of the-invention will-ube apparentfrom the followingdescription taken in-oonjunc-* tiers-with theaccompanying drawinginwhich:

1 is an exploded view :in-perspective f- I an'eleotrodynamic instrumentembodyingthe 111- vention;

Fig=2 is-aview:intperspective; w ithzparts broken awe/wotamelectrodynamic-sinstmnnent"embody ingestmodified formof thecinventiom.

' Fig; .3 isa--schematic vviewil-lustra-tlng suitableoonnectionsf-orthe-electricalsinstrument of Fig; 1:;-

Fig. 4 is a plan view, withportions-brokenawam or anelectrody-namic"instrument illustratinga further modification-Of"the*;inVeH=tiiOn;;=t3/Hd .FigbS is at vie-w in plan of 1 anelectrical instru-- merit-representing -afurther modification oftheinvention.-

Referring to the drawing; Figplushows amelec trodynamieinstrumenthaving,a: stator assembly I and a'r'otorassembly 3; The f'I OtOI aSSBmbIY M-eludes-a shaft 5, whichmounted for rotation relative-to-the statorassembly by means of suitable bearing screws 'I- and 9which-aresecured-to the statorassembly. The-shaft 5 has attachedtheretoa moving coil assembly'which" comprises a-.coil- 'l l.- Thiscoil-=hasterminals connected; re-

' 'itl is',.ithereiore sansoliiect ofithe inventionto spectivelytothelinner endsaottwoiflexible,spiral;

cured to terminal lugs I9 and 2|, which are secured to the statorassembly but which are insulated therefrom.

In order to damp rotation of the rotor assembly, an electroconductivedisk 23 is secured to the shaft 5. This disk rotates between the polesof a permanent magnet 25 to damp rotation of the rotor assembly in amanner well understood in the art.

The rotor assembly is biased in a predetermined direction by means of acontrol spring 21 having its inner end attached to the shaft and havingits outer end secured to a lever 29 which is pivotal about the bearingscrew 1. Pivotal movement of the lever 23 is employed for adjust ing thezero position of the rotor assembly in a manner well understood in theart.

Rotation of the rotor assembly 5 may be em-- ployed in various ways, as,for example, to actuate electrical contacts for relaying purposes andfor actuating pointers associated with a scale for indicating the extentof movement of the rotor assembly relative to the stator assembly. Forthe purpose of illustration, a recording pen 3! is attached to the shaft5 for rotation therewith. This pen moves across the face of a chart 33to leave a record of the movement of the rotor assembly on the chart.The chart 33 may be advanced continuously or intermittently in a man-'-ner well understood in the art for providing a record of quantitiesmeasured by the rotation of the rotor assembly.

In order to develop torques between the rotor and stator assemblies,magnetic fields are provided for two coil sides Ila and llb of the coilll. These magnetic fields may be developed in response to currentsflowing, respectively, in fixed windings 35 and 31. When current flowsin the coil H, the reactions between such current and the two magneticfields associated with the coil sides Ha and Nb result in theapplication of torques to the shaft 5 which are dependent on themagnitude of the current in the coil H and the magnitudes of thecurrents in the fixed windings 35*and 31. v

In order to provide a compact and efiicient electrodynamic instrument, amagnetic structure is provided which includes a magnetic section 39.This magnetic section comprises a magnetic core 4|,which has a passage43 therethrough dividing.

the magnetic core "into two inner pole pieces 45 The inner pole piece 45is spaced fromand 41. anouter'pole piece 49 to provide an air gap 5|within Whichthe coil side Ha is positioned for rotation. The outer polepiece 49 has a neckpassing through thefixed winding 35 and is connectedto theinner pole piece 45 by means of a magnetic connector 53. It willbe noted that the outer polepiece 49, the air gap 5!, the inner pole'piece 45 and the magnetic connector 53 define a magneticpathfor-magnetic flux produced by current flowing in the winding 35.This magnetic path is represented in Fig. 1 by a dotted line 55.

In a somewhat similar manner, an outer pole piece 51 is spaced from theinner pole piece 4'5 to define an air gap 59 within which the side llbof the coil H is positioned for rotation. The outer pole piece 51 has aneck passing through the fixed winding 31 and is connected to the innerpole piece 41 by means of a magnetic connector 4 6!. Consequently, theouter pole piece 51, the magnetic connector 6 I the inner pole piece 41and the air gap 55 define a path' for magnetic flux produced by currentflowing in the fixed winding 3 which is indicated by a dotted line 53.

In order to permit the utilization of short air :gaps and to permitaccurate centering of the coil II, it is desirable that the inner andouter pole pieces be permanentlyand rigidly associated with each other.Such association is accomplished in the embodiment of Fig. 1 by means ofa connecting element 65 extending between the outer pole piece 49 andthe inner pole piece 41. Conveniently, the entire magnetic section 39may be constructed from a plurality of similar unitary laminations ofsoft magnetic material which are united to each. other by means ofsuitable rivets- Each lamination is accurately punched from 51. a sheetof magnetic material to provide portions of the pole pieces 45, 41, 49and 51, the connectors 53 and GI and the element 65.

It will be noted that the magnetic paths 55 and 63 are substantiallymagnetically independent or: The magnetic paths represented by thedotted lines 55 and 63 are united by a coneach other.

necting element 55 which for convenience is made of magnetic material.However, by inspection of Fig. 1, it will be noted that magnetic fluxesproduced by currents flowing in thewindings 35 and 31 flow in separatemagnetic paths provided by the magnetic section 39.

to remove the coil II from th'e'magnetic section 39, the permanentmagnet 25 and the bearing screw 1, together with'its support, may beremoved and the strips I3 and 15 may be disconnected from the lugsIQ'and 2 l. The rotor assem..

bly is then rotated in. a clockwise direction, as viewed from thecontrol-spring end of the shaft 5, to its extreme position wherein thecoil II is alignedwith the passage 43. The rotor assembly may then bemoved in a direction parallel to v the shaft 5, free of the magneticsection 39. A

reverse procedure may be followed for reinserting the coil in operativeposition relative to the magnetic section 33.

Although the structure of Fig. 1 thus far specifically described may beemployed for measuring purposes, some error may be introduced bysolenoid action, Such action maybe understood by considering the eiiectof current passing through the coil II when the fixed windings 35 and 31are deenergized. It will be noted that the paths 55 and 53 areasymmetric with respect to the paths of rotation of the coil sides H aand lib. When current passes through the coil H, the coil seeks aposition such that the magnetic reluctance offered to magnetic fluxproduced by current flowing in the coil l I is a minimum. For theinstrument of Fig. 1, solenoid action produced by the magnetic section39 tends to urge the rotor assembly in a counterclockwise direc-Consequently, the magnetic fields produced in the air gaps 5| and 59 inFor this reason, the

In ci 'd to reduce or eliminate errors introduced by 'solenoidactiom themagnetic structure fFig. 1 in'ciucesa secondm'aeneticsection 59 Whichis-eXa-Gfly similar-iii construction to the magnetic section "39; andparts thereof are identified by similar reference characters. However,it will be-iiotd that themagnetic section 69 is-revei sedrelative'tothemagnetic section 39 about an ail-is transverse 1910 the Shaft 5-. Thismeans that the solenoid forces applied by the two magnetic sections tethe coir- H are oppositely directed, and "the -i=esu ltantsolenoid forceis substantially reduced- "or eliminated. This con-- struction forieduc-ing or eliminating solenoid ac-. tlon is disclosed in the aforesaidLunas applica- The magnetic sections 39 and B9 are spaced apart forcertain purposes; Such spacing pre-- Vents the shortcircui-tin'g 'ofportions of the magnetic s ections- Which. are at different magneticpotentials. In 'additiomthe sections are spaced apart by a distancesuflic-ientto permit rotation of an end not th'ecoil- I therebetween.This facilitates reinovat of the coil ll from operative positionrelative-to the magnetic structure and the return of the coil M tooperativeposition without disturbing the: magnetic structure.

To understand the procedure for removing the coil- I t, let it beassumed'that it isdesired toremove the coil 11 from operative position. Thecoil "H first' i's bta'ted wits-extreme position in aclockwise-direction; as viewed from the controlspring ehd-ofthe Shaft;This-brings the coil H intoalig-nment"with the passage 43 of themagnetic-section 39. It willbe note'd that the connector 65islocatedoutside thepassage 43- and outside'the p'ath ofthe-mtiil-g afid'does not interme with the-desired removal or the coil. With the coil inalignment with the passage; 43; the rotoig-assenibly may be moved in adirection parallel to the shaft 5* until-the end He of" theceirengagestnemagneuc section 69; It will beuiid'e'i'stood thatthepermanent magnet 25 and the bearing crewl and its-support first shouldBe removed, and the serpen -amt I5 should be disconnectedrein the lugsHand '2'! priortosu'ch axial movement of the rotor assembly.-

Wi-t-h the end 11a of thecoil'intermediate the two magnetic section's'39and 89; the rotor assembiy rqta'ted to its extreme position in acodnterclockwise direction as viewed from the control spring end of theshaft-to bring the coil assembly into argument-with the passage 43; ofthe magnetic section 69: rotor assembly then may bemcted in adirectipnparalleltd the haf 5:: o, remo ethecdilt ii'c mh etely from t mn ic ti n flt n f 'he associa d: m gn structure. Ajrever'se sequence maybe followed fionreturnjing the'c'oil" H to it's-operative positigil.Itwill' he; noted that. during" such removal, and; return or the coil;the associated magnetic structurefis' not disturbed; This is desirablefor the, reason. that any disturbance :or the magnetic structure mayresult in achange in the calibration of theinstrumnt:

Conven'iently, the 'ina'gneti'c' sections. 39" and 6.9 maybe spaced bymeans of spacers H and 13; If of'mag netie material; the" spacers shouldbe so configuredthat' they do not short: portions of the magnetic sectwhich are intende d 'to operate at different ma eticpoteirtials.Ifdesir'edhoweverg the" s p 1 as; may 'be i'iiade' or non-magneticmaterial; Preferably; the spacers" are located only at the ends of themagnetic sections in order to facilitate inspection of the clearancebetween the pole pieces "of the magneti'c section 38 a'ndthe pole piecesof the magnetic section 69. The magnetic structure of Fig. I is shown inassembled condition in Fig. 2; The magneticsections, together with theassociated spacers, maybe se-- cured to each other by means of-"suitablerivets 15.

It will be noted that the-inner pole pieces are of" taperedconfiguration. For instance, the pole piece 45 tapers from apredetermined cross section adjacent the magnetic connector 53 to asmaller cross section adjacent the opposite end of the inner pole piece-451 Inasmuch as the magnetic flux decreases with the decrease in crosssection, such configuration maintains a substantiallyuniform fluxdensity-in the inner pol'e piece and provides a l'arge passage: 43. 7

Circuit connections suitable for theinstrument oi Fig. l are illustratedin Fig. 3. In Fig; 3. a three-wire circuit having conductors Ll, L2 andL3 are shown. These may be the conductors of a single phase, 'threewirecircuit or the conductors ofa three-wire; direct current circuit. Inthemajority of such circuits; voltage unbalance between the outerconductors and neutral are not undulylarge. I

It will be noted that the winding 35 of the instrument is disposed forenergization in accordancewith current-flowing through the outer conductor L3. Thewi'nding 311 or the instrument is disposed: forenergi'zation in accordance with current-flowing in the outerconductorLl. The coil II is connected-for energization through asuitable impedance; such as a resistor IL in ac o'ordance with thevoltage between the outer conductors LI and No connection ismade to theneutral cOnductorLZ. With the connections illustrated in Fig; 3, theinstrument would measure the power fiow ing inthe three-wire circuit.

The modification illustrated in Fig; 2 is-exactlysimilar'to that ofFig'; I except forthe construction of the moving coil' assembly. In Fig;2 the movin coil assembly includes twoindependent coils 19 and 8|. Thesecoils are "spaced ahlgularly about a common portion of the shaft 5 toposition one side of the coil 19 in the airgap 5t and one side of the:coil '81 in the air gap 58. Since these coils are sub'stahtiall3equidistant from a plane transverse tothe axis ofthe rotation thereof,the instrument of Fig. 2 may be termed a coplanar. instrument; The'coil19 may have its terminals connectedto spiral conductor strips similar tothe strips l3'and Hiof Fig. 1. In asi-milar manner; the coil 8] mayhaveits terminal connected to two additional conductor strips (not shown),Thisconstruction permits independent energization of the two coils T9,81.

Consequently, the instrument of Fig; 2 is the '70 two coils.

equivalent of a prior art two-element electrodynamic" instrument" andmay be employed similarly. One element would include the coil, l9 andthefixed winding 35, whereas the second'el'einent would. include thecoil 81 and the fixed winding 31.

It will be noted that one side of each of the coils I9 and 8| is,adjacent the shaft 5. This means that some coupling may exist betweenthe Such coupling would not be objectionable for the application of theinstrument to Fig. 2 to direct-current circuits or for many applicationsof'the instrument to measurement of quantities inalternating-currentcircuits. However, this coupling may be minimized bysuitable spacing of the coils from each other or suitable shielding asdesired. The coil assembly of Fig. 2 may be removed from operativeposition with respect to the associated magnetic structure and returnedto operative position in the same manner discussed with reference to thecoil ll of Fig. 1.

The instrument of Fig. 4 is similar to the instrument of Fig. 1, exceptfor the configuration of the air gaps associated with the coil assembly83, and the omission of the control spring 21 of Fig. 1. This coilassembly 83 may be similar to the coil II of Fig. 1 or the coil assemblyof Fig. 2. However, for the purpose of discussion it will be assumedthat the coil assembly 83 corresponds to that of Fig. 1. It will benoted that the instrument of Fig. 4 provides an air gap 5I a whichincreases from a predetermined length A to a longer length B. In asimilar manner the air gap 59a increases from a length C, which may beequal if desired to the length A, to a longer length D, which may beequal to the length B.

Let it be assumed that the coil assembly 83 is energized in accordancewith a predetermined quantity and that the winding 35 is energized toproduce a torque urging the rotor assembly in the direction of the arrowE. Let it be assumed further that the winding 31 is energized to urgethe rotor assembly in the direction of the arrow F. The rotor assemblythen will seek a position wherein the torques applied thereto inresponse to current flowing through the windings and 31 are equal. Ifsuch a condition is illustrated in Fig. 4 and if the current through thewinding 35 should decrease for any reason, the rotor assembly wouldrotate in the direction of the arrow F. Such rotation carries the coilside disposed in the air gap 5Ia into a stronger portion of the magneticfield. At the same time the movement of the rotor assembly carries thecoil side disposed in the air gap 59a into a weaker field. The rotationof the coil continues until the torques are again balanced.Consequently, the instrument of Fig. 4 may be considered a ratio-typeinstrument. Applications for instruments of this type are known intheart.

As pointed out in my copending application, Serial No. 685,057, filedJuly 20, 1946, the construction of a magnetic structure to permit theinsertion of a coil assembly therethrough into operative position and topermit removal of the coil assembly from operative position withoutdisturbing the magnetic structure permits the utilization of complexmagnetic structures. For example, in Fig.5 a magnetic structure isdisclosed wherein four air gaps are provided for two separate coils of acoil assembly I90. These coils 19a and Sla correspond to the coils I9and 8| of Figure 2 except for the additional radial spacing of the coilsfrom the associated shaft 5. Such spacing renders negligible thepreviously mentioned coupling between the two coils.

For providing magnetic fields within which the coils 79d and Illa aredisposed for operation, a magnetic structure In! is provided whichincludes two magnetic cores I03 and I85. The coil #90. surrounds themagnetic core I53 whereas the coil 8Ia surrounds the magnetic core $5.The magnetic cores are concentric about the shaft 5 and form, in effect,a resultant annular magnetic core having a diametric passage I91extending therethrough. The passage is proportioned to permit movementof the coil assembly I00 therethrough in a direction parallel to theshaft 5.

The magnetic core I03 has a first magnetic pole piece I09 spaced fromthe outer surface of the core to define an air gap III therebetween. Oneside of the coil 19a, is disposed for rotation through this air gap. Asecond magnetic pole piece H3 is spaced from the inner surface of themagnetic core I03 to define an air gap II5 within which a second side ofthe coil 19a is disposed for rotation. In a similar manner, the magneticcore I05 is provided with a first magnetic pole piece Ill and a secondmagnetic pole piece H9 to define air gaps l2l and I23 for reception oftwo sides of the coil 8Ia.

The magnetic structure IIlI includes a magnetic ring I25 whichsubstantially surrounds the pole pieces and magnetic cores and which ismagnetically connected to each of the pole pieces and magnetic cores.For example, the magnetic cores I03 and I05 are connected to themagnetic ring by means of magnetic connectors I21 and I29. to themagnetic ring through magnetic connectors I3I and I33. It will be notedthat all portions of the magnetic structure are clear of the passageIlll and do not interfere with removal of the coil assembly through thepassage in a direction parallel to the shaft 5 through the passage. Eachof the four air gaps III, H5, I2I and I23 communicates with the passageID! to permit rotation of the coil 19a and 8Ia in a counterclockwisedirection as viewed in Fig. 5 into the passage I0! for removaltherethrough.

In order to establish magnetic fields in the air gaps, the fixedwindings 35 and 31 surround respectively the magnetic connectors I29 andI21.- As examples of suitable polarities, the windings 35 nd. 31 whenenergized may produce north poles N and south poles S as indicated inFigure 5. If the windings are energized by alternating currents, theindicated polarities are instantaneous polarities.

In order to segregate further the magnetic circuits associated with thewindings 35 and 31, the magnetic ring I25 may be provided with anopening I31. Since the magnetic circuits are independent, the coil 19aand the winding 31 may be energized independently of the winding 35 andthe coil 8| a to provide a two-element electrodynamic instrument.

. The magnetic structure lIlI may be formed of similar magneticlaminations secured to each other by means of rivets I39. Eachlamination may be punched accurately from a sheet of magnetically softiron or steel.

If it is desired to compensate the instrument of Figure 5 for errorsintroduced by solenoid action, the magnetic structure may be dividedinto two sections; each similar to the section or magnetic structure IOIillustrated in full lines in Figure 5, but reversed with respect to eachother about the line AA. The two sections IOI and mm are associated withthe same coils 19a and Ma and with the same fixed windings 35 and 31 inthe manner discussed with reference to Figure 2. In order to avoidconfusion, the added section IBM is shown in broken lines in Fig. 5.

In operation the instrument of Figure 5 may be connected in conformancewith the connections employed for any conventional prior art two-elementelectrodynamic instrument. For example, if the instrument is associatedwith a twophase alternating current circuit, the coil 19a may beenergized in accordance with the voltage across a, first phase while thefixed winding 31 I is adjusted in accordance with the current fiow- Thepole pieces H3 and H9 are connectedtasse ta the-name i iara o sa d @011s des t aste 'sq s eid W at s" 6f. the? @9711 eans, the asymmetries oilthengi agntic paths a sqqi sq'w t iea 9 31 f R i en celli'ri 'said sitelyfd'l ,cted'for. ubstantially. M g forfdirecting 9 bat s as es sele o dt m e ed easiest ma n ti a arg es t e mas Q a d' io sat s:

I n ele @3 1 mea s; a

a n s-sesam mi wt s ams inns mst t un tieacivt v. r. s pals. a mien as em /ne t en: e wi a st vane mite -ass mb com i n t seemed var abl Q fir tmagne ic field o a i alhc independent, f 7 aid: fi st- 1am, ca sand; sesonsieeto a third v able y for establishing a second magnetic field I v lec nd Bast en oaths coi whe eby ro a m ans i 111 a i 994 ii 'ii si dfibe ween Qi he soil isa inaction o saidthneaqu ti ie 39 sai 11,111?! P9?g by e P' -1th 'Q is t s ia a m aaaestrieai in tmment re pon ive t a tath the s il were ted the att str an e iuna iene thr -va i e uantitie astat r as? Path. am le a roteress ibis-comp ising a co me ns I as eletric l iris wm ata a 9 2 i a un ta y the. spit. tor notati n rela v tohe ma n c Si it s i inn ls stator ly about an axisjmeans or e er: issesWi 95% at P9 ie s fietd R iiis nathe so l inieceesdance with a firstvariable bei ma ate He w e n. a i 9 quantity, field means responsive toa second varip fi fi 1 E9 able quantity?forfestablisliing a firstmagnetic D16 spag a fisld itafits ett enef soi ,and field mea s se s? eide i sa d a magnetically iridependentbt' said fir t-named toindependent means includ field ansassi rs nonsive s a thi d variableeiie. ma n ti fle hr Quantity for establishing a second magnetic fieldfor a, second portion of the .coil, whereby rotation V p I L eithe"'coilis a. function of saidthree quantities, inte e sia eidiwqs is. Saidt n-a m ly havin p e therein 45 be n adjacent se s. 9 2 PH Pfi t 9 l fifi through which the. coil is. removable from operaa, passage hrough Wheh h toil may be mo ed tive position without disturbing the means forHam 3 fit t session e .1 to, sa d m g etic establishin saidmagnetic..fields. structure, to, a, second p here a d 911 3,. In. aneleotricalinstrument, a stator assemmay e m afigq miig j a P, stemm dPat bit, a rotor! assembly comprising coil" means, 56 to enter saidsides oi said coil in the air gaps, means mounting. the coil meansfn'rirotation'relasaid magnetic structure including magne ic tivetoc'theistatorrassembly about an axis; said means hiQI- whe S id QQ n, Sid con stator assembly, comprising a unitary magnetic position, extendsbetween said inner 1 P16 member having two magnetically-independent bypath which is eggte znal to both the coil and magnetic paths eachincluding an arcuate air gap the predetermined path.

positioned to receive a coil side of the coil means, In an electricalinstrument; coil means desaid magnetic member having a passage throughsigned for rotation about an axis intermediate which the coil means maybe removed from optwo sides thereof; a pair of magnetic structures,erative position without disturbing said magnetic each having twomagnetically-independent magpaths. 60 netic parts, each of said sides ofthe coil means 4. In an electrical instrument, a stator assembeingassociated with a separate one of the magbly, a rotor assemblycomprising coil means, netic parts of each of the magnetic structure,means mounting the coil means for rotation relathe magnetic partsassociated with each of said tive to the stator assembly about an axisintersides defining paths for magnetic flux produced mediate two of thecoil sides, said sides being 55 by current flowing in said coil meansfor proequidistant from any point on the axis, said stator ducingsolenoid forces acting between the parts assembly comprising a firstunitary magnetic and the coil means, pairs of said magnetic parts memberhaving two magnetically-independent be ng reversely associated with thecoil means to magnetic paths each including an arcuate air produceoppositely directed solenoid forces actgap positioned to receive aseparate one of said ing between the coil means and the magnetic coilsides of the coil means, andasecond magnetic parts to decrease theeffects of said forces on member having two magnetically-independentmovement of the coil means. magnetic paths each including an arcuate airgap 8. In an electrical instrument, a magnetic positioned to receive aseparate one of said coil structure, coil means, and means mounting thesides, said magnetic paths being asymmetric with coil means for rotationrelative to the magnetic structure about an axis, said axis beinglocated intermediate two sides of said coil means, said sides beingequidistant from any point on the axis, said magnetic structurecomprising a pair of magnetic cores each having a separate partpositioned between said axis and each of said sides of the coil means, afirst one of said magnetic cores having a passage permitting movement ofthe coil means therethrough in a direction substantially parallel tosaid axis when said coil means is adjacent a first extreme of its pathof rotation, and asecond one of said magnetic cores having a passagepermitting movement of the coil means therethrough in a directionsubstantially parallel to said axis when the coil means is adjacent asecond extreme of its path of rotation, magnetic means cooperating withsaid magnetic cores for establishing a separate magnetic path having anair gap for each of said sides of the coil means, said magnetic pathsbeing magnetically independent of each other, and separate meansassociated with each of said magnetic paths for establishing a magneticfield in each of said air gaps.

9. In an electrical instrument, a magnetic structure, coil means, andmeans mounting the coil means for rotation relative to the magneticstructure about an axis, said axis being located intermediate two sidesof said coil means, said sides being equidistant from any point on theaxis, said magnetic structure comprising a pair of magnetic cores eachhaving a separate part positioned between said axis and each of saidsides of the coil means, a first one of said magnetic cores having apassage permitting movement of the coil means therethrough in adirection substantially parallel to said axis when said coil means isadjacent a first extreme of its path of rotation, and a second one ofsaid magnetic cores having a passage permitting movement of the coilmeans therethrough in a direction substantially parallel to said axiswhen the coil means is adjacent a second extreme of its path ofrotation, said magnetic cores being spaced apart in the direction ofsaid axis by a distance sufiicient to permit movement of an end of thecoil means therebetween, magnetic means cooperating with said magneticcores for establishing a separate magnetic path having an air gap foreach of said sides of the coil means, the magnetic path for each of thesides of the coil means including the two parts of the magnetic coresadjacent the associated side of the coil means, said magnetic pathsbeing magnetically independent of each other, and separate meansassociated with each of said magnetic paths for establishing a magneticfield in each of said air gaps, said magnetic paths being spaced fromsaid passages and the space between the magnetic core to permit movement01 the coil means through said passages and space.

10. A magnetic structure for an electrical instrument comprising a pairof spaced first and second inner magnetic pole pieces, a first outermagnetic pole piece spaced from the first inner magnetic pole piece todefine therewith a first airgap, a second outer magnetic pole piecespaced from the second inner magnetic pole piece to define therewith asecond airgap, said pole pieces having pole faces giving said air-gapsarcuate configurations about a common axis, said airgaps be ng spacedangularly about the axis, a magnetic connector establishing the onlymagnetic path between the first pole pieces, a magnetic connectorestablishing a magnetic path independent of the first-named magneticpath between the second pole pieces, and a connector completing aconnection between the inner pole pieces by a path external to theairgaps and the space between the inner pole pieces, said airgaps andthe space defining a continuous Z-shaped passage.

11. A magnetic structure as claimed in claim 10 in combination with asecond magnetic structure similar to the first-named magnetic structure,said structures being reversed relative to each other about a linetransverse to the axis and being axially spaced from each other alongthe axis.

CECIL L. FREEDMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

